ERP recordings, which are extracted from electroencephalography (EEG) recordings made at the scalp of electrical activity in the brain, can reflect the brain's responses to sensory and cognitive events with millisecond precision, he said. But the electrical brain activations detected with ERPs are harder to trace back to their exact origins inside the brain.
To overcome these limitations, Grent-'t-Jong and Woldorff combined brain responses from the two technologies recorded in identical experiments.
"To effectively understand how the brain accomplishes cognitive functions, it is critical to be able to delineate both the brain regions that are involved and the timing and sequence of their activations," Woldorff explained.
In the experiments, participants were asked to keep their gaze directed toward the center of a computer screen. They then were presented with a series of four-second trials, each beginning with the appearance of an "instructional" letter cue that the participants had been coached on how to interpret. For example, participants might be shown an "L" cue instructing them to focus their attention "covertly" -- that is, without moving their eyes -- to a location on the left side of the screen.
Most such letter cues instructed participants to direct their attention to a specific location on the screen and be alert for a possible faint dot "target" that might appear there during the following second or two. During some trials, however, the cue directed participants not to orient their attention to a particular location because no target would be appearing on that trial.
In all of the trials, participants had to decode and interpret the meaning of the instructional letter cue. But only in response to attention-directing cues did particip
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Contact: Monte Basgall
monte.basgall@duke.edu
919-681-8057
Duke University
3-Jan-2007